1. Field of the Invention
The invention generally relates to transillumination imaging instrumentation used in the biological setting and, more particularly, to improvements in the design of transillumination imaging devices to prevent scattered light from adversely affecting detection performance, and provide a more useful format for imagery.
2. Description of the Prior Art
Transillumination involves the use of non-ionizing radiation, preferably having wavelengths ranging from 500 nm to 1500 nm, to image an object. Similar to an X-ray, transillumination involves passing radiant energy through an object, and detecting transmitted or reflected radiation. Detection can be accomplished using photocells or other electronic devices, or using photographic film or other image capturing materials. However, particularly when biological imaging is being performed (i.e., breast imaging, teeth imaging, etc.), transillumination offers the advantage of non-ionizing radiation compared to the ionizing radiation used in X-rays which is now widely believed to cause the induction of various cancers. However, one of the drawbacks of using non-ionizing radiation is that it is more easily scattered than ionizing X-rays, thus making it difficult to detect small structures in an object being imaged.
U.S. Pat. No. 4,945,239 to Wist et al., which is herein incorporated by reference, describes several concepts for distinguishing light which passes straight through a sample from light which is scattered from other sources. One method involves using a pair of pin-hole boxes in front of and behind the object being imaged whereby scattered light must traverse straight though spaced apart pin holes in order to reach a detector. Another method involves separately activating an emitter-detector pair, among a plurality of pairs in an array, whereby the timing of activation of the selected emitter-detector pair is used to assure that the light beam passes straight through an object. A variation on this method is to use shutters in front of a detector module whereby the timing of opening the shutter is matched to light emission from a specific emitter. The shutter scheme contemplated in Wist et al. can also be matched to the time of flight of the light through the object. Still another method involves positioning matched polarization filters on either side of an object, whereby scattering events that occur within an object change the plane of polarized light such that it no longer matches the filter positioned in front of a detector and the scattered light is not detected. Phase plates with a plurality of adjacent polarized regions can be used in combination with emitter and detector arrays, thereby eliminating the need for mechanically moving a light source.
In recent years the use of three dimensional modeling or imaging has become a useful and popular tool in many fields including the medical field. This popularity is due in part to the increased ability of computers to receive and process large amounts of raw data required for three dimensional images. Transillumination imaging is useful not only for detection but for providing detailed locations of anomalies in body parts. Using transillumination to form a three dimensional image provides more information than would be possible with a mere two dimensional image. The present invention can be configured in one of several ways to yield the data required by a computer to produce a three dimensional image of a semi opaque object such as a leg, foot, breast, or tooth, and to detect anomalies therein. Furthermore, the present invention drastically reduces the size of the imaging equipment and reduces the time required to make images.
Articles which demonstrate the utility of transillumination in biological and medical applications include: Wist et al., IEEE Transactions on Medical Imaging, Vol. 12, No. 4, December, 1993 (pages 751-757); Wist et al., J Clin. Laser Med. In Surgery, 11:313-321 (1993); Wist et al., J. Clin Laser Med. In Surgery, 12:165-170 (1994); Swineford et al., Proceedings of Clinical Applications of Modern Imaging Technology II, SPIE, Vol. 2132, pp.201-207 (1994); Wist, SPIE 2628:286-299 (1995); and Wist et al., SPIE, 2389-552-563. These articles show the use of transillumination scanning technology in detecting incipient caries in teeth and identifying objects in tissues.